Sewanhaka High School

SCIENCE 234

Everything about Equations
A chemical equation contains a lot of information. Many equations show evidence of a chemical change such as
a change in temperature (exothermic – give off heat; endothermic – absorb heat), release of a gas, or formation of
a precipitate. Other identifying characteristics of a chemical equation such as a change in color or a change in odor
cannot be demonstrated in the equation. Some changes and/or conditions are shown using symbols such as [1] solid
precipitate – (s) or 9; [2] liquid – (R); [3] gas – (g) or 8; [4] dissolved in water or aqueous – (aq); [5] heat – );
[6] electricity – elec.; and [7] light – b#. Symbols and formulas that are neither reactants nor products are written
above or below the yield sign (ÿ). Examine the equation below:
2KClO3(s) 2KCl(s) + 3O2(g)
MnO 2(s)
∆
The equation tells us the following: [1] The reactant is KClO3; [2] KClO3 is a solid; [3] KClO3 decomposes,
particularly when heated ()) in the presence of the catalyst MnO2; [4] One of the products is KCl, a solid; [5] The
other product is O2, a gas. [6] Conservation of mass is shown because the reactants contain 2 atoms of K, 2 atoms
of Cl, and 6 atoms of O, and the products contain 2 atoms of K, 2 atoms of Cl, and 6 atoms of O also.
Sometimes a reaction results in the formation of a precipitate from dissolved reactants. Examine the equation
below:
K
2SO4(aq) + Ca(NO3)2(aq) ÿ 2KNO3(aq) + CaSO4(s